1. Field of the Invention
This invention relates to the field of syringe pumps, in which syringes are placed with their plungers connected by syringe holders to the drive mechanisms of the pumps that push the plungers of the syringe barrels at a controlled rate to force the contents of the syringe out at a controlled rate into tubing that leads to a patient, research animal or analytical apparatus.
2. Description of the Related Art
Generally, syringe pumps are known in the medical arts as well as in biological, experimental psychological research and biotechnology industry. Their use includes the dispensing of medications or solutions to patients, research animals and for accurately dispensing for later mixing of fluid compounds for analysis (e.g. blood analysis) and in cellular (e.g. cloning) and tissue culture research where dispensing very small and accurate volumetric amounts is required.
Examples of prior art devices in the field are disclosed in the following U.S. Patents.
U.S. Pat. No. 4,563,175 discloses a syringe pump that houses three syringes and the associated separate drive mechanisms for the delivery of fluids from each of the syringes of various volumetric capacities. This pump is intended for use in patients and for administering several fluids at different rates. Fluid volumes delivered are in the milliliter range. The pump, though intended for human use, contains no fluid or electrical swivel to prevent binding and blockage of flexible tubing. The central drive screw employed in this machine is not a true worm gear, but rather a central drive screw that frictionally engages the helical threads of a central drive member and, thereby, moves an attached arm that depresses a plunger on a housed syringe. This is distinctly unlike my invention that employs two micro-syringes, has an electrical swivel, employs two oppositely turned threaded rods that convert the rotary motion of a central drive screw to linear motion by frictional engagement with the threads of the drive screw and push the plungers of the bilaterally arranged micro-syringes.
U.S. Pat. No. 6,248,093 B1 discloses a cylindrical piston pump that incorporates a rotating drive screw (split lead screw design) and internally threaded cylinder. In this design, an attached motor turns the drive screw, which engages the threads of an internal segment that advances a middle and outer segment that together to expel fluid from the cylinder. The screw drive mechanism works in one cylinder only. The amount of fluid moved is not in the micro-liter or nano-liter range but in the range required for human pharmaceutical delivery which is generally in the cubic centimeter or milliliter range. No fluid or electrical swivel is employed. Drive mechanism is significantly different from the three member threaded rod mechanism of my invention in which two separate threaded rods are moved linearly by the frictional engagement of their threads with the threads of the rotating central drive screw. The device disclosed in U.S. Pat. No. 6,248,093 is not intended or can it be applied to research animal use wherein animal subjects can move freely while self-administering micro-liter or nano-liter volume amounts; its use is limited to human drug administration. My invention can be used in both human and animal applications and can be incorporated in analytical apparatus as a result of its very small size, unlike the device in U.S. Pat. No. 6,248,093. That machine also requires an O ring for water sealing, whereas the pump of my invention does not.
U.S. Pat. No. 6,475,188 discloses a bilateral micro injector pump for freely moving animals in an operant chamber. The pump employs a stepper motor and a central screw drive mechanism. A recirculating micro-ball bearing slide and guide are employed as a frictionless carrier for the plunger depressing block. Block and ball-bearing slide comprise a xe2x80x9ckneexe2x80x9d that converts the rotary motion of the stepper motor into linear motion and depresses the plungers of two micro-syringes arranged in parallel. The pump uses an electrical swivel to deliver electricity to the drive mechanism. The pump extrudes from nano-liter to micro-liter volumes from both micro-syringes simultaneously. The pump also contains an electrical swivel that allows the pump to move as the animal freely behaves so that the flexible tubes do not become bent or bound up and, thereby, restrict the flow of fluid. In response to the assertion that the ball-bearing slide and guide may allow microscopic lateral xe2x80x9cplayxe2x80x9d in the linear drive mechanism, and that the xe2x80x9ckneexe2x80x9d itself may bind with the threaded hole in the knee and, thereby cause intermittent interruption in the smooth continuous and accurate movement of the syringe plungers and consequent problematic and inaccurate extrusion of fluid from the syringes, I developed my present invention. My invention overcomes this asserted problem by a completely different mechanism that is illustrated in FIG. 1 of this application. A three member drive apparatus whose threaded rod components move without friction with the pump housing; there is friction only where the central drive screw meets the two threaded rods (where rotary motion is converted to linear motion). The invention also eliminates the size, weight, lateral xe2x80x9cplayxe2x80x9d, and drive screw/knee binding problem of the machine is U.S. Pat. No. 6,475,188 while, at the same time, delivering unit nano-liter volumes from both micro-syringes simultaneously and incorporating an electrical swivel for movement of the pump without constriction and consequent obstruction of fluid flow through the flexible tubing that delivers fluids to freely behaving subjects.
U.S. Pat. No. 4,846,797 discloses a syringe positioning device that holds four syringes in parallel. It employs classical rack and pinion gears that are connected to and depress the plungers of the syringes. That design is quite different from the three threaded rod component design of the drive mechanism in my invention illustrated in FIG. 1. The positioning system of U.S. Pat. No. 4,846,797 is not a true pump but only the positioning system. Its motor drive was not disclosed. It is not intended for animal use and is not capable of delivering micro-liter or nano-liter volumes. It does not contain a fluid or electrical swivel. It is also much larger than my invention.
U.S. Pat. No. 5,423,752 discloses a hand held variable proportion dispenser that is actuated manually by the patient administering the medication. Two separate medications can be dispensed together from the same outlet needle. The drive mechanism utilizes a screw positioning mechanism that allows the patient to set the amount to be self-administered. The dispenser is not intended for any use other than human manual medication administration. The screw set mechanism is significantly different from the drive mechanism employed in my invention illustrated in FIG. 1.
A micro-pump for administration of fluid compounds to freely behaving animals is provided. The drive mechanism of the pump contains a screw drive mechanism that overcomes the limitations of prior art devices discussed in the Background of the Invention section of this application. In the preferred embodiment, the micro-pump provides enhanced control over the accurate dispensing of from nano-liter to micro-liter volumes of fluid compounds to freely moving animals. It is therefore an object of this invention to provide a device for the delivery of accurate and identical volumes of fluids from two syringes simultaneously.